Ultrasonic flow sensors are used in particular for measuring the volumetric flow or mass flow or the flow rate of a gaseous or liquid medium flowing through a pipe. A typical ultrasonic flow sensor includes two ultrasonic transducers in offset position in the direction of flow, the transducers generating ultrasonic signals and emitting them to the other ultrasonic transducer, which receives them. As a function of the emission direction, the ultrasonic signals are either accelerated or decelerated by the flow. The ultrasonic signals are therefore received by the two transducers after different propagation times. An analysis electronic system is finally able to calculate the desired measured value from the propagation time difference of the ultrasonic signal in the direction of flow and of the ultrasonic signal in the opposite direction.
Another type of ultrasonic flow sensor utilizes the effect of beam drift. Normally, this type includes two transducer arrays positioned opposite from one another on a pipe (series positioning of a plurality of transducers), one of which functions as an emitting array and the other as a receiving array. The emitting array sends an ultrasonic signal to the opposite receiving array where the signal is detected. If a fluid flows through the pipe at a flow rate v, the sound waves emitted transverse to the direction of flow are carried along by the flow and thus diverted in the direction of flow (beam drift). The structure of such an ultrasonic flow sensor having two transducer arrays is relatively expensive and complex.